Structural components made of fiber reinforced plastic materials, for instance sandwich structures such as panels, may take up moisture which needs to be removed again. Moisture take-up is especially a problem in sandwich structures in which a honeycomb core structure with honeycomb cells is covered on both sides by skin layers made of fiber reinforced laminates. These skin layer laminates are made of a matrix material having embedded therein glass fibers, carbon fibers, or aramid fibers and these laminates close the core cells in which moisture may accumulate over time due to capillary ducts in the skin layers through which water may enter into the hollow cells.
The capillary ducts can be formed by micro-cracks that may be naturally present in the fiber reinforced panels or these cracks may be formed during service of these panels. For cost reasons, it is not desirable to replace entire panels that have taken up moisture and repair is preferable, for example, by applying one or several further skin layers to repair the leaks, whereby the additional skin layers would also be made of fiber reinforced plastic materials. However, before such repair can be made, it is absolutely necessary to first remove the moisture or water from the inner volume of the structural component. If the water or moisture is not removed, delamination of the panel structure is unavoidable because the temperatures at which the additional skin layers must be cured are in the range of about 120.degree. C.-180.degree. C. and the water would start boiling at these temperatures so that delaminations between the honeycomb cell core and the skin layers is unavoidable.
It is known to dry fiber reinforced structural components in conventional drying ovens in which heat is supplied and which drying may even take place at reduced pressures in order to remove water that is molecularly bound in the matrix of the fiber reinforced material. However, the just mentioned known method is not suitable for removing water that has entered through the above mentioned capillary ducts into the sandwich structure, especially if that water has accumulated in the honeycomb cells.
The drying at elevated temperatures has the further drawback, that the drying temperatures and/or the lowering of the reduced pressure has its limitations because it must be avoided that the water comes to a boil inside the laminated structure, thereby destroying the structural component primarily by delamination.